A substrate processing chamber typically communicates with a substrate transfer chamber through a sealable opening that is both wide and relatively short to accommodate insertion and removal of horizontally-oriented substrates. It is known to use a slit valve to seal such an opening. For example, a sealing plate of the slit valve may be extended to seal the opening, and retracted to permit passage of substrates through the opening. Slit valve designs that avoid the problems of (1) particle generation through rubbing friction, and (2) uneven compression of resilient sealing elements, are preferred.
During certain types of substrate processing steps, a pressure differential may exist between the processing chamber and the transfer chamber such that high pressure within the processing chamber pushes outward against the sealing plate of the slit valve. The slit valve thereby is subjected to stresses and fatigue, the amounts of which increase with the pressure differential. Pressure differential effects are exacerbated when large substrates, such as those employed for flat panel displays, are involved (e.g., as a larger substrate requires a larger opening between the processing chamber and transfer chamber and a larger sealing plate to seal such an opening). Conventional slit valves typically are not designed to accommodate large pressure differentials. Accordingly, a need exists for improved methods and apparatus for sealing an opening of a processing chamber, particularly when large pressure differentials are being employed.